Asphalt is commonly used as a paving material for road construction and maintenance. Typically, asphalt, often referred to as “asphalt binder” or “asphalt cement,” is mixed with aggregate to form material used in asphalt paving. Processing and use of this material by paving crews yield asphalt pavement. The asphalt pavement comprises aggregate held within a continuous phase of the asphalt binder by adherence of the asphalt binder to the aggregate.
The strength and durability of the asphalt pavement depends on various factors such as the properties of the materials used, the interaction of the various materials, the mix design, construction practices, and the environmental and traffic conditions to which the pavement is exposed. To produce a mix that will have good performance during the lifetime of the pavement, it is important to attain proper coating of the aggregate with the asphalt with the optimum asphalt binder film thickness, good adhesion of the asphalt onto the aggregate, and good cohesive strength of the asphalt.
Conventional pavements suffer from various types of distress modes such as permanent deformation. Permanent deformation is a significant problem for asphalt pavement. A road may be about 80 to about 100° C. or more warmer in the summer than it is in the winter. At warmer temperatures, asphalt pavement softens and can creep and move creating ridges and ruts, often referred to as “rutting.” Rutting of the asphalt pavement can occur under the weight of heavy trucks or traffic that has temporarily stopped, such as, for example, at a traffic light intersection, since rutting is dependent on both the weight of the vehicle and the time duration of the weight application.
To reduce or prevent rutting, polymers or other materials having a relatively higher modulus than the asphalt, or that can produce a higher modulus asphalt binder at higher temperatures than the unmodified asphalt, are often incorporated into conventional asphalt binders. Typical polymers used to modify asphalt binders to reduce or prevent rutting include elastomers, such as, for example, styrene/butadiene/styrene copolymer (SBS), and plastomers, such as, for example, polyethylene, ethylene/vinyl acetate copolymer (EVA), and the like. Compared to elastomers, some plastomers have several advantages such as, for example, low viscosity and better workability at both the asphalt fabrication plant and at the paving construction site. As a result, low temperatures can be used to process asphalt and also to pave roads. This results in significant environmental and economic benefits. Another material used to produce higher modulus asphalt binders is polyphosphoric acid (PPA). In many cases, however, the use of this material is limited due to corrosivity issues, reports of premature cracking of pavements constructed with binders modified with PPA and in some cases outright bans. Plastomers are more easily handled than PPA and do not have the corrosivity issues
Recently, the Multiple Stress Creep Recovery (MSCR) test has been developed to evaluate an asphalt binder's rutting resistance. Properties that can be evaluated by the MSCR test are the non-recoverable creep compliance, Jnr, and the stress sensitivity, Jnr,diff. For certain plastomers, while they may meet Jnr standards (and traditional Performance Grade (PG) standards for that matter), their stress sensitivity parameters Jnr,diff are higher than the allowed maximum value and, as a result, these plastomers should be used in combination with elastomers to meet specifications. However, in these cases, the workability benefits of the plastomers may disappear, that is, for example, higher temperatures may have to be used to process the asphalt and also to pave the roads. This could lead to serious environmental pollution and could dramatically increase energy costs.
Accordingly, it is desirable to provide asphalt binders with plastomers such that the asphalt binders meet MSCR criteria. In addition, it is desirable to provide asphalt binders with plastomers that result in asphalt binders that meet MSCR criteria without requiring elastomers. It is further desirable to provide asphalt paving material that includes such asphalt binders and that are useful without substantially increasing environmental pollution or energy costs. It also is desirable to provide methods for fabricating such asphalt binders. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.